Merges orders_helper functionality inside has_orders concern

Both these objects where using/setting a variable called valid_orders.
As a results, some specs where becoming flacky
(features/budgets/investments_spec.rb, balloting phase). By putting
them together, there is no `valid_orders` variable any more (everything
is @valid_orders) and the flackyness is gone.

app/controllers/concerns/has_orders.rb

@@ -4,8 +4,8 @@ module HasOrders
   class_methods do
     def has_orders(valid_orders, *args)
       before_action(*args) do |c|
-        valid_orders = valid_orders.call(c) if valid_orders.respond_to?(:call)
-        @valid_orders = valid_orders
+        @valid_orders = valid_orders.respond_to?(:call) ? valid_orders.call(c) : valid_orders
+        @valid_orders.delete('relevance') unless params[:search].present?
         @current_order = @valid_orders.include?(params[:order]) ? params[:order] : @valid_orders.first
       end
     end